Hi Sara,
Good to know you got it working. Different force fields have
different parameters, hence different equilibrium energies, bond
distances, forces and stiffnesses. It is normal that systems behave
differently with different parameters.
It would be best to choose a force field file that is proper for your
model. If you are plotting the E-V curve for diamond, ffield.reax.cho
is most likely a good choice. You should check the publications for
more info.
Best,
Ray